Electronic commutation of currents



Aug. 7, 1945. M|THELL 2,380,982

ELECTRONIC COMMUTATION OF CURRENTS Filed NOV. 12, 1942 PHASE SHIFT ATTORNE Y v 1940, comprising a and other electrodes arrangedconcentrically Patented Aug. 7; 1945 uNrrso s'r-Arss PATENT OFFICEmcraomo co Dorm Mitchell,

Bell Telephone mmrsrrou or Boundlrook', 8.1., signer to New York, N. Y.,a museum of New York Application November 12, 1942, Serial No. ceases50mins.

The present invention relates to the commutation or electrical currentsfor signaling or other purposes, including electronic or other type ofcommutation.

An object of the invention is to eliminate or reduce ripple -.or otherdistortion effects such as may be caused, in the case of an electroniccommutator. by the fact that the moving electron beam has finite width.1

Electronic' switching -or commutation is favored in some typesofjtransmission systems speed at which because of the almost unlimitedthe beam may be rotated.- This speed may exseed mam times overthehighest speed possible with mechanical commutators. A- drawpressed on acommutator with the result that amplitude variations n the commutatedcur- .rents representing ripple and similar disturbances can be reducedin the process or convertcathode l2. The beam is caused to rotate by ingback to the amplitude pulses that are to be used for transmission.

Reference 'will now be made to the following detailed description andthe accompanying drawing for a more complete understanding of theinvention, together with itsvarious objects andfeatures.

The single figure of the drawing shows a schematic circuit diagram of aterminal of a an accelerating grid l4, shields ll, control grids ii, anda common anode il, the latter being in the form of a cylinder. Thesurroimding envelope is not shown. Positive voltage is applied to theaccelerating grid 14, shields II and anode i'I from suitable taps onbattery 20, the negative pole of which is shown grounded as is also thea rotating magnetic field generated in field coils two of which areshown at 2| and 22 supplied with alternating current of suitablefrequency from generator 23. A phase shifter, such as a quarterphasenetwork 24, is connected in circuit with the field coil II toprovide the necessary phaseshift'for generating the required rotatingfield.

As the beam Ii rotates it strikes the shields II in succession andthese, shields have the effect of cutting-oil the electron current tothe anode ll momentarily while the beam is incident upon them. Pulsesoi' anode current are produced when the beam falls between two of theshields i5 and is allowed to strike the anode i1. During the time whensuch an output pulse is being generated, the strength of the beam and,therefore, the strength ofv the output pulse can be modulated by placingvariable potentials on the control grids it. These control grids areshown connected in pairs with respective pairs connected to the outputof individual frequency modulators 4, 5, 6, etc. If desired, individualgrids may be connected to the frequency moduators instead of connectingthe grids in pairs.

'l'he connection of the grids in pairs illustrates one way 'that a tubehaving a greater number of electrodes than the number of lines to beserved may be used,'by connecting pairs or groups of multiplextelephonesystem embodying the invention in anillustrative form.

Referring to the drawing, a number of separate telephone lines shown asextending from individual microphones i, 2, 3, etc. are connected .4through respective frequency modulators I, ll,

etc. to electrodes of an electron commutating tube II which has arotating electron beam ii adapted to sweep over electrodes of the tube.

The tube It may be of the type disclosed in Skellett Patent 2,217,774,granted October 15, centrally located cathode 12 thereabout. Theseelectrodes comprise, proceeding-in order from the cathode l2 outwardly,

the grids in common to any one line. The grids i6 receive an initialbias, usually negative, from common grid bias battery 25. v

A high frequency oscillator 26 is shown connected in common to all .ofthe frequency modulators so that the mean frequency of thefrequency-modulated waves produced in the varius-frequency modulators isthe same throughout; These frequency modulators may be reactanee controltubes of a type well known in the art, an example being disclosed inPatent 2,076,264 'to Chireix et al., granted April 6, 1937.

Another type of frequency modulator that may be used comprises asaturable core inductance and rectifier, this type being disclosed, forexple. in L. R, Wrathall, application Serial No.

354,357, filed August 2'7, 1940, which matured into Patent No.2,311,796, February 2;, 194a.

2 s,s so,oss

Outputcurrentfromtheanodellpasses through the primary winding of outputtransformer ll and into a heterodynlng detector 20 supplied with"heterodyne oscillations from source it for stepping the frequency of thefref uency-modulated waves down to a convenient sent signals. use offrequency meme- .tion, however, as described, these smplitude'var-'iations are greatb reduced provided they are not or desired level.Detector 20 is followed by an" amplitude limiter it after which comeaslope circuit ll, amplitude detector 38 and low-pass filter 34 leadingto the outgoing transmission line SI.

In the operation of the system as shown in the drawing, speech wavesfrom diflerent talkers produced in microphones I, I, 3, etc. effectfrequency modulation oi waves supplied from the common oscillator 28 andthe respective frequency-modulated waves are applied to indi-.

vidual pairs of control grids It. As the beam sumcient to shut oif'thespacecurrent completely. This is because the amplitude limiter II servesto wipe out such-chsngesin amplitudeasareproducedbythetypeotvariationsmentioned. caused by movement of theradial beam across the tube electrodes. Further, it is to be noted thatoverlap produced .by the beam strikon two neighboring-grids at the sameinstant, which might result in cross-talk, is reduced since such effectwill disappear as soon as a diflerence of 6 decibels or more in strengthappearsbetween the two signals.

The invention is not to be construed as limited to the particularcircuit arrangements that H rotates past the shields It and comes inbetween a pair of shields the strength of the beam is varied inaccordance with the frequency-modulated wave on the respective grid It,setting up a corresponding frequency-modulated wave in the outputtransformer 28. These frequencymodulated waves occurring in spurts orpulses have variable frequencies representing signal modulations. Theirfrequencies are stepped down in the detector stage 2! and amplitudevariations occurring in the pulse envelope are largely eliminated by theamplitude limiter circuit 3| which can be arranged to limit the maximumamplitude of the transmitted wave to as small a value as may be desiredin accordance with well-known practice in the reception offrequency-modulated waves. The slope circuit 32 converts thefrequency-modulated waves into waves of variable amplitude so that theyare capable of detection in the amplitude detector 38. In this way aseries of pulses comprising frequency-modulated waves are converted to aseries of amplitude pulses or direct current pulses a varying inamplitude in accordance with the respective signal variations. Low-passfilter 34 ,may be provided to suppress undesired carrier components orother undesired amplitude peaks or variations representing distortionare largely eliminated; The transmitted pulses may, therefore, bereceived by any suitable type of time division multiplexreceiver, suchas that shown in Fig. 12 of the Skellett patent, or in the patentreferred to. It will be understood that the commutating means used toreceive the messages from the transmitter shown. in the drawing must beoperating in proper synchronism and phase with respect to the beam Ii.

As explained above, the beam H has a flnite width or thickness so thatas the beam passes over the various electrodes .in the tube I I amhavebeen disclosed herein for illustrative purposes but the scope is definewhich follow.

What is claimed is: 1. In a signal commutating circuit, means totranslate signals into frequency modulated waves, a rotary beamelectronic commutator tube having beam modulating electrodes and anoutput circuit, meansto place the frequency-modu-' lated wave potentialson said electrodes in accordance with the signals to cause a frequency-'modulated wave to appear in saidoutput circuit whenever said beam sweepspast a beam modulating electrode, means to remove incidental amplitudevariations from said frequency modulated waves appearing in said outputcircuit, and means in said output circuit for detecting saidfrequency-modulated waves.

2. In a signaling system, a plurality of signal input circuits, a rotarybeam electronic commutator tube, having input electrodes arrang'ed'toexert successive controfion said beam, an' output .circuitfor said tube,means to translate signals in said input circuitsinto frequencymodulatedwaves and to impress the latter on respective control electrodes of saidtube'whereby to set,

up frequency-modulated waves in said output circuit in successivetimes,-and means insaid v output 'circuit for removing incidentalamplitude variations from said output wavesand thereafter convertingsaid output waves into varying amplitude signal currents.

3; In a signal system, signal input circuits, a rotary beam electroniccommutator having a beam adapted to move past a succession of controlelectrodes, a common anode and output circuit therefor, a source of highfrequency oseillations, means to modulate the wave-length of a said highfrequency oscillations by signals in said input circuits, means-toimpress the modu-. lated oscillations on respective control electrodeswhereby to produce in said output circuit wavelength modulatedoscillations representing said signals in successive times, and means toconvert said output oscillations into amplitude var-v iations includingan amplitude limiter ahead of plitude changes will occur in thespacecurrent depending to a considerable extent upon whether the platehitsthebeam squarely or is partly cut oil by one of the shields It. Inan ordinary amplitude modulated system in which,v for example, thespeech signals are directly applied .to the grids It. thesevariations'inthe space current would. introduce components of noise intothe the converting means. 1

4. In a rotary-beam electronic commutator having control electrodes forsuccessivelymodulating the strength of the beam in its rotation and acommon output circuit,"'means for reducing distortion of input wavesarising from the fact that the beam has a width comparable to the widthand spacing of said control electrodes comprising means for firstconverting inputcontrol waves to wave-length modulations of highfrequency oscillation and means to impress the' latter on said controlelectrodes, and means in inthe claims said output circuit for removingamplitude variations from the wave-length modulated oscillations andconverting said oscillations into varying amplitude currents.

5. In a, signal transmission system, sources of signal waves, means tofrequency-modulate a high frequency wave in accordance with each signal,a common transmission path, a commutator for switching thefrequency-modulated waves into said common transmission path insuccession, means in said common path for suppressing amplitudevariations in the waves in said path, and means in said common path todetect the frequency-modulated signals.

DOREN MITCHELL.

